Tag: interpolation

I know, I’ve posted a few of these, but a new video came out showing the descent of Curiosity to the surface of Mars that’s worth a look.

YouTube user "hahahaspam" did a clever thing. The Mars Descent Imager (MARDI) is a camera that points straight down, past the rover, so engineers on Earth could later see the exact path Curiosity took on its way down to the Martian surface and also get an overview of the area. It took a series of images that were later put together to make various animations (see Related Posts below). The motion appears jerky because the camera only took about four pictures per second.

What hahahaspam did was interpolate between the frames, making the motion appear much more smooth. The animation he made is really quite wonderful:

Nice, huh? Interpolation is a math term that involves estimating the value of something between two measurements. A simple example involves someone running. You measure their progress: after one second they’ve traveled 2 meters, and after two seconds they’ve run 4 meters. How far did they get in 1.5 seconds?

Obviously, the answer is 3 meters. It may not be exact – a person’s running speed might change – but it’s probably close. There is a precise mathematical way to do interpolations like this, and that’s what hahahaspam did. Digital pictures are really just long strings of numbers, and video is the same thing except each pixel value changes with time. All you need to do is take two frames taken some time apart, then interpolate the value at each pixel for what it would be halfway between the time of the first frame and the second, and boom! You’ve made a video with twice the frame rate and the motion looks smoother.

It’s actually a lot harder than this in practice (rapid brightness or color changes makes this more difficult and less accurate, for example), but I hope this gives you the idea of how it works. The result in this case is pretty cool. Hahahaspam also created a side-by-side comparison of the original and interpolated videos, too, so you can see how they look together.

Very nice! And well done. I think it’s great that so many folks are so inspired by this that they want to play with the data. It really shows how much this has affected people.